CN116519163B - Fiber-based spring FP (Fabry-Perot) cavity temperature sensor, method and system - Google Patents

Abstract

This application proposes an optical fiber-based spring FP cavity temperature sensor, method and system, including a single-mode optical fiber and a 3D micro-nano structure fixed on the end face of the single-mode optical fiber, and also includes: The glass tube outside one end of the nanostructure; the heat-sensitive material filled in the glass tube; wherein, the 3D micro-nano structure includes a disk cavity plate set for the end face of the single-mode fiber, a ring base connected to the end face of the single-mode fiber, and a connection One or more elastic return parts of the disc cavity plate and the ring base, and an FP cavity is formed between the end face of the single-mode optical fiber and the disc cavity plate; wherein, the length of the elastic return part changes due to the thermal expansion of the heat-sensitive material, so as to The red shift of the interference spectrum is brought about to realize the temperature measurement; in addition, the adjustment of the temperature sensitivity can also be realized by adjusting the elastic constant k of the elastic reset member. The application has the characteristics of good stability, high processing precision and customizable sensitivity.

Description

An optical fiber-based spring FP cavity temperature sensor, method and system

technical field

The present application relates to the technical field of optical fiber sensors, in particular to an optical fiber-based spring FP cavity temperature sensor.

Background technique

A fiber-based Fabry-Perot (FP) cavity temperature sensor is a common fiber optic sensor used to measure temperature changes. It uses the Fabry-Perot interference effect in the optical fiber to achieve temperature measurement.

In the sensor, a special optical fiber is made into a Fabry-Perot cavity, usually by fabricating two reflective surface structures on the optical fiber. When light passes through the cavity, part of the light will be reflected back to form interference, and the characteristics of the interference are related to the length of the light path in the cavity. Changes in temperature cause small changes in the length of the fiber, which in turn alters the optical path length and thus the characteristics of the interference. By measuring characteristic parameters of the interfering light, such as changes in light intensity or light frequency, changes in temperature can be deduced. In general, spectroscopic analyzers can be used to measure parameters of interfering light.

Therefore, fiber-optic-based Fabry-Perot cavity temperature sensors are widely used in many fields, including industrial control, oil and gas industry, energy system monitoring, medical equipment, etc. They provide a reliable solution for precise temperature measurement.

However, traditional all-fiber FP cavity temperature sensors usually have low sensitivity (~10pm/°C), which greatly limits their further applications. In recent years, researchers have increased the temperature sensitivity of the device by 1-2 orders of magnitude by filling the interior of the FP cavity with heat-sensitive materials such as ethanol, ultraviolet glue, and polydimethylsiloxane (PDMS). However, currently reported devices of this type usually suffer from poor stability, low processing precision, and difficult alignment of reflective surfaces.

For example, Kunjian Cao et al. (Compact fiber biocompatible temperature sensorbased on a hermetically-sealed liquid-filling structure, Kunjian Cao, Yi Liuand Shiliang Qu, 27 Nov 2017/Vol. 25/Optics Express/29597) reported an ethanol-based The optical fiber FP cavity temperature sensor is mainly prepared by continuously welding two sections of capillary glass tube (SCT) on the end face of a single-mode optical fiber, and injecting ethanol into the first section of the tube. Its sensitivity can reach 429pm/℃. However, ethanol in a liquid state reduces the device stability, and the multiple welding process is complicated and time-consuming.

Bowen Li et al. (High-sensitivity temperature sensor based on ultravioletglue-filled silica capillary tube, Bowen Li, Yinggang Liu, Xiaoya Song, Haiwei Fu, Zhenan Jia and Hong Gao, 21 Nov 2020/Vol.67/Journal of ModernOptics/1327 ) reported a fiber optic FP cavity temperature sensor based on UV glue filled SCT structure. The device is obtained by inserting a single-mode fiber into the SCT structure, injecting UV glue into the interior and curing it. Its sensitivity can reach 963pm/℃. However, it is difficult to precisely control the cavity length for this device, resulting in low processing repeatability.

Jin Li et al. (Microfiber Fabry-Perot interferometer used as temperature sensor and an optical modulator, Jin Lia, Zhoubing Lia, JuntongYanga, Yue Zhanga, Chunqiao Ren, 29 April 2020/Vol.129/Optics and LaserTechnology/106296) reported a A fiber optic FP cavity temperature sensor with a PDMS-filled SCT structure. The device is obtained by encapsulating two single-mode optical fibers in the SCT at the same time, and then filling the inside with PDMS and curing. Its sensitivity is as high as 6.386nm/°C. However, the device has the problem that the two fibers are difficult to align precisely, which affects the device performance.

In addition, temperature sensors based on FP cavity interference usually have a design contradiction between sensitivity and effective range, that is, the higher the sensitivity, the lower the effective range. Therefore, in practical applications, it is necessary to select sensors with different sensitivities for different application scenarios. For example, a high-sensitivity sensor is suitable for high-precision detection of temperature fluctuations in a narrow range; while monitoring temperature changes in a wide range requires sacrificing a certain degree of sensitivity. However, the currently reported fiber optic FP cavity temperature sensors usually only have a fixed sensitivity and are applicable to a single scenario, which cannot effectively solve the contradiction between sensitivity and effective range.

Therefore, there is an urgent need for a new fiber optic FP cavity temperature sensor with customizable sensitivity to solve the problems of poor stability, low processing accuracy, difficult alignment of the reflective surface, and inability to customize the sensitivity of the existing sensors.

Contents of the invention

The embodiment of the present application provides an optical fiber-based spring FP cavity temperature sensor, which aims to solve the problems of poor stability, low processing precision, difficulty in aligning the reflective surface, and inability to customize the sensitivity existing in the current technology.

The core technology of the present invention is mainly to use 3D micro-nano structure and heat-sensitive material to drive the length change of the elastic reset part through the thermal expansion of the heat-sensitive material, thereby causing the red shift of the interference spectrum and realizing the measurement of temperature. By adjusting the 3D micro-nano structure The elastic constant k realizes the adjustment of temperature sensitivity.

In the first aspect, the present application provides a fiber-based spring FP cavity temperature sensor, including a single-mode fiber and a 3D micro-nano structure fixed on the end face of the single-mode fiber, and also includes:

A glass tube set outside the end of the single-mode optical fiber with a 3D micro-nano structure;

heat sensitive material filled in the glass tube;

Among them, the 3D micro-nano structure includes a disc cavity plate set for the end face of the single-mode fiber, a ring base connected to the end face of the single-mode fiber, and one or more elastic reset members connecting the disc cavity plate and the ring base, An FP cavity is formed between the end face of the single-mode fiber and the disc cavity plate;

Wherein, the adjustment of its elastic constant k is realized by adjusting the geometric dimension of the elastic reset member;

Wherein, the length of the elastic reset part is driven to change by the thermal expansion of the thermally sensitive material, so as to bring about a red shift of the interference spectrum.

This setting has the following effects:

Temperature sensitivity: The length of the elastic reset part changes due to the thermal expansion of the heat-sensitive material, thereby changing the optical path length of the FP cavity, resulting in a red-shift of the interference spectrum. The extent of this redshift correlates with changes in temperature, allowing the sensor to measure changes in temperature in real time.

High precision: By adjusting the elastic reset part in the 3D micro-nano structure, the elastic constant K can be adjusted, thereby changing the sensitivity of the optical fiber cavity. Through reasonable design and adjustment, high-precision temperature measurement can be realized.

Reliability: Optical fiber-based sensors have the advantages of high temperature resistance, corrosion resistance, and electromagnetic interference resistance, and can operate stably for a long time in harsh environments to provide reliable temperature measurement.

In this way, the sensor has good stability and high processing and detection precision.

Further, the heat-sensitive material is cured after filling.

With this setting, the following effects can be achieved:

Stability: By curing the heat-sensitive material, it is ensured that it retains its fixed shape and properties during sensor use. This prevents the material from deforming or leaking under temperature changes, thus ensuring the stability and reliability of the sensor.

Mechanical support: The cured heat-sensitive material can provide mechanical support for the 3D micro-nano structure and enhance the structural stability of the sensor. It maintains the relative position and geometry of the fiber to other components, ensuring that the sensor's performance is not affected by external vibration or displacement.

Thermal actuation: The thermal expansion of the heat-sensitive material can effectively drive the elastic reset member to change its length and cause a change in the length of the optical fiber cavity. This increases the sensor's sensitivity and response to temperature changes, providing more accurate temperature measurements.

Protection and Encapsulation: The curing operation securely encapsulates heat-sensitive materials in glass tubes, protecting them from damage and contamination from the external environment. This can prolong the service life of the sensor and improve its corrosion resistance and anti-interference ability.

Further, the 3D micro-nano structure is prepared by two-photon polymerization 3D printing process.

With this setting, the following effects can be achieved:

High precision and complexity: Two-photon polymerization 3D printing is a high-resolution printing technology that can achieve precise printing at the micron level. This makes it possible to fabricate complex micro-nano structures, such as disk cavity plates, ring bases, and elastic reset members. Through this process, the size, shape, and geometric features of micro-nanostructures can be precisely controlled to meet specific sensor design requirements.

Customized design: Two-photon polymerization 3D printing has good flexibility and customization capabilities. According to the requirements of specific sensors, personalized design and custom manufacturing can be carried out. This flexibility enables the sensor to be adapted to different application needs, achieving better performance and applicability.

High stability and repeatability: Two-photon polymerization 3D printing has good stability and repeatability, which can ensure the consistency of the manufactured micro-nano structures in size, shape and performance. This is critical to making high-quality sensors, ensuring their performance is stable and reliable.

Rapid manufacturing: Compared with traditional processing methods, two-photon polymerization 3D printing is a rapid manufacturing technology. It can quickly convert the designed micro-nano structure from a virtual model to a physical body, greatly shortening the manufacturing cycle and delivery time.

Further, when there are multiple elastic reset members, they are evenly arranged along the circumference of the ring base.

With this setting, the following effects can be achieved:

Uniform force distribution: The uniform arrangement of the elastic return elements allows for an even force distribution on the ring base. This provides more stable force transfer and uniform strain distribution, ensuring uniformity and consistency in sensor performance.

Reduce strain concentration: By arranging multiple elastic return parts evenly on the ring base, the concentration of strain can be reduced. The uniform distribution of strain reduces the risk of fatigue and damage to the material, extending the lifetime of the sensor.

Enhanced Structural Stability: The uniform arrangement of the elastic return helps to enhance the structural stability of the sensor. It can balance the effect of force, reduce structural deformation and stress concentration caused by non-uniform load, and improve the stability of the sensor and the ability to resist external interference.

Improved temperature uniformity: The uniform placement of the elastic return improves the sensor's uniform response to temperature. When the temperature changes, the change in the length of the elastic reset member will also be uniformly distributed, so as to maintain the uniform change of the optical fiber cavity and improve the accuracy and consistency of temperature measurement.

Further, each elastic reset member is helical.

With this setting, the following effects can be achieved:

Elastic Restoration Force: The helical elastic reset piece has a relatively large elastic restorative force. When subjected to an external force, the elastic reset member can undergo elastic deformation and has the ability to return to its original state. This helps maintain the stability and accuracy of the sensor.

Stable force transmission: The helical elastic return can provide stable force transmission. They can evenly distribute stress when stressed and transfer it to other components, such as disk cavity plates and optical fibers. This helps keep the sensor's structure stable and reduces performance variations caused by force non-uniformities.

Improve elastic adjustment ability: the helical elastic reset member can adjust the elastic characteristics by changing the size, elastic coefficient and winding method of the helix. This makes it possible to adjust the elastic constant k as needed to meet different temperature measurement requirements. This adjustability enhances the sensor's flexibility and adaptability.

Good thermal actuation performance: The helical elastic return usually has a large surface area and contact surface, which helps to increase the contact area with heat-sensitive materials. When the heat-sensitive material thermally expands, the helical elastic reset member can be driven more effectively, causing the length of the optical fiber cavity to change, thereby realizing temperature measurement.

Further, the outer diameter of the elastic reset member is larger than the inner diameter of the ring base and smaller than the outer diameter of the ring base.

Further, the heat-sensitive material is polydimethylsiloxane.

With this setting, the following effects can be achieved:

Fast Cure: Polydimethylsiloxane has fast heat cure properties. When polydimethylsiloxane is heated under set conditions, it can rapidly change from liquid to solid state. In this way, the curing process can be completed in a shorter time and the production efficiency can be improved.

Good heat resistance: Polydimethylsiloxane usually has good heat resistance, and the heat resistance temperature after curing is as high as 200°C. This makes them stable in high-temperature environments, which is especially important for temperature sensors in high-temperature applications, ensuring operational stability and long life of the sensors.

Excellent chemical resistance: Polydimethylsiloxane has good chemical resistance and has good resistance to many chemicals. This enables the sensor to maintain stability and accuracy in environments affected by chemical substances, improving the usability and adaptability of the sensor.

In a second aspect, the present application provides a method for preparing the above-mentioned optical fiber-based spring FP cavity temperature sensor, comprising the following steps:

S00, using two-photon polymerization 3D printing technology to print 3D micro-nano structure on the end face of single-mode optical fiber;

S10, encapsulating the 3D micro-nano structure in a glass tube, injecting heat-sensitive materials and placing them in a vacuum box to allow the heat-sensitive materials to enter the FP cavity;

S20, thermally curing the heat-sensitive material, so that the heat-sensitive material is completely cured, and the preparation is completed.

Further, in step S00, the processing parameters of the two-photon polymerization 3D printing process are:

The two-photon laser parameters used are wavelength 780nm, laser power 16.5mW, and laser scanning speed 170μm/s;

The developing agent that development adopts is propylene glycol methyl ether acetate;

The cleaning solution used for cleaning is methyl nonafluorobutyl ether;

The wavelength of violet light used for photocuring is 405nm, the curing temperature is 25°C, and the curing time is 10min.

With this setting, the following effects can be achieved:

High-precision preparation: The two-photon polymerization 3D printing process can achieve high-precision preparation, and can accurately print the required 3D micro-nano structure, including the disc cavity plate, the ring base and the elastic reset piece. This helps ensure sensor accuracy and performance stability.

Tight packaging and injection: Encapsulating the 3D micro-nano structure in a glass tube and injecting heat-sensitive materials can achieve tight packaging and fixing. This ensures that the thermally sensitive material can completely fill the FP cavity and be in close contact with the 3D micro-nanostructures for accurate temperature measurement and transfer.

Heat-cured materials: Injected heat-sensitive materials can be fully cured by heat-curing them. This ensures the stability and reliability of the heat-sensitive material during sensor operation. The cured heat-sensitive material can maintain its shape and performance, and is not affected by the external environment except temperature.

High production efficiency: High production efficiency can be achieved by using two-photon polymerization 3D printing process and thermal curing preparation method. The 3D printing process enables fast and precise preparation, while the thermal curing process can be completed in a relatively short time. This helps improve the manufacturing efficiency and throughput of sensors.

In the third aspect, the present application also provides an optical fiber-based spring FP cavity temperature sensor system, including a tunable laser, an optical fiber connector, an optical power meter, and any one of the above-mentioned optical fiber-based spring FP cavity temperature sensors ; The tunable laser is connected to the first end of the optical fiber connector, the second end of the optical fiber connector is connected to the optical power meter, and the third end of the optical fiber connector is connected to the spring FP cavity temperature sensor.

This setting has the following effects:

Temperature measurement: By using an optical fiber-based spring FP cavity temperature sensor, the system can achieve high-precision measurement of the ambient temperature. The sensor uses the principle of optical interference to determine the temperature change by monitoring the red shift of the interference spectrum and provide accurate temperature data.

Tunable laser: The tunable laser in the system can provide a controllable laser light source, which can be scanned and selected in different wavelength ranges to adapt to the working requirements of different sensors. This makes the system more flexible and adaptable.

Optical fiber connector: The optical fiber connector plays the role of connecting different components to ensure the transmission and coupling efficiency of optical signals. It provides a reliable fiber optic connection to ensure efficient communication and data transfer between the sensor and other components.

Optical power meter: The optical power meter is used to measure the power of the optical signal, and is used to analyze and record the change of the optical power output by the sensor. Through the use of optical power meters, temperature changes can be monitored and recorded in real time, providing accurate temperature measurement results.

System integration and portability: The optical fiber-based spring FP cavity temperature sensing system has small volume and weight, which is easy to integrate into other devices or systems. This makes the system portable and can be widely used in various environments and scenarios.

The main contributions and innovations of the present invention are as follows: 1. Compared with the prior art, the spring FP cavity in the temperature sensor of the present application is directly prepared on the end face of the optical fiber by using two-photon polymerization 3D printing technology, which has high processing precision. The reproducibility of device fabrication can be ensured. After the spring FP cavity is filled with liquid heat-sensitive materials, the stability of the device can be guaranteed after thermal curing and glass tube packaging;

2. Compared with the prior art, the temperature sensor of the present application has customizable sensitivity. By adjusting the elastic constant k of the elastic reset member, the sensitivity of the temperature sensor can be effectively adjusted within the range of 100-700pm/°C.

The details of one or more embodiments of the application are set forth in the accompanying drawings and the description below, so as to make other features, objects, and advantages of the application more comprehensible.

Description of drawings

The drawings described here are used to provide a further understanding of the application and constitute a part of the application. The schematic embodiments and descriptions of the application are used to explain the application and do not constitute an improper limitation to the application. In the attached picture:

FIG. 1 is a schematic structural diagram of a fiber-based spring FP cavity temperature sensor provided by the present invention.

Fig. 2 is a flow chart of the preparation of an optical fiber-based spring FP cavity temperature sensor provided by the present invention.

Fig. 3 is a schematic diagram of an optical fiber-based spring FP cavity temperature sensing system provided by the present invention.

Fig. 4 is a schematic diagram of the working principle of the optical fiber-based spring FP cavity temperature sensor provided by the present invention.

Fig. 5 is a schematic diagram of the interference spectrum of an optical fiber-based spring FP cavity temperature sensor (prepared with spring constant k=9.9μN/μm) and the displacement of the trough position with temperature changes provided by the present invention.

Fig. 6 shows the test results of repeatability and stability of an optical fiber-based spring FP cavity temperature sensor provided by the present invention.

Fig. 7 is the test result of the relationship between the sensitivity and the spring constant k of the optical fiber-based spring FP cavity temperature sensor provided by the present invention.

Fig. 8 is the relationship between the spring constant k and the structural size of the optical fiber-based spring FP cavity temperature sensor provided by the present invention.

In the figure, 100, single-mode optical fiber; 101, glass tube; 102, disc cavity plate; 103, ring base; 104, spring structure; 105, heat-sensitive material.

Detailed ways

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, the same numerals in different drawings refer to the same or similar elements unless otherwise indicated. Implementations described in the following exemplary embodiments do not represent all implementations consistent with one or more embodiments of this specification. Rather, they are merely examples of apparatuses and methods consistent with aspects of one or more embodiments of the present specification as recited in the appended claims.

It should be noted that in other embodiments, the steps of the corresponding methods are not necessarily performed in the order shown and described in this specification. In some other embodiments, the method may include more or less steps than those described in this specification. In addition, a single step described in this specification may be decomposed into multiple steps for description in other embodiments; multiple steps described in this specification may also be combined into a single step in other embodiments describe.

Existing sensors of this type have problems such as poor stability, low machining accuracy, difficult alignment of reflective surfaces, and inability to customize sensitivity.

Based on this, the present invention solves the problems existing in the prior art by combining heat-sensitive materials and 3D printed elastic return parts.

Embodiment one

This application aims to propose a fiber-based spring FP cavity temperature sensor, specifically, referring to FIG. 1 , which includes a single-mode fiber 100 and a 3D micro-nano structure fixed on the end face of the single-mode fiber 100, and also includes:

A glass tube 101 sleeved outside one end of the single-mode optical fiber 100 with a 3D micro-nano structure;

The heat-sensitive material 105 filled in the glass tube 101;

Wherein, the 3D micro-nano structure includes a disc cavity plate 102 arranged on the end face of the single-mode fiber 100, a ring base 103 connected to the end face of the single-mode fiber 100, one or more of the disc cavity plate 102 and the ring base 103 A plurality of elastic return parts, an FP cavity is formed between the end face of the single-mode optical fiber 100 and the disk cavity plate 102 .

Preferably, the disc cavity plate 102 is aligned with the center of the end face of the single-mode fiber 100, parallel to the end face of the single-mode fiber 100, and the diameter of the effective reflection surface is larger than the mode field diameter of the fiber.

Preferably, the elastic return member is a helical spring structure 104, which is used to connect the ring base 103 and the disc cavity plate 102. The number of spring structures 104 is one or more. In this embodiment, the number of spring structures 104 is three. and are evenly arranged along the circumferential direction of the ring base 103 and the disc chamber plate 102. Uniformly arranging the elastic reset member on the ring base 103 can achieve uniform force distribution, reduce strain concentration, and enhance structural stability. This helps to improve the performance and reliability of fiber-optic-based spring FP cavity temperature sensors.

In this embodiment, the length of the spring structure 104 is 20-80 μm, the diameter is larger than the inner diameter of the ring base 103 and smaller than the outer diameter of the ring base 103 , and the cross section of the spring wire is circular or square. The elastic constant k of the spring structure 104 is between 1 and 150 μN/μm. By selecting springs with different elastic constants, the temperature sensitivity of the sensor can be effectively adjusted within the range of 100 to 700 pm/°C.

Preferably, the annular area of the ring base 103 is an area to avoid light beams, and its inner diameter is larger than the mode field diameter of the optical fiber, so as to ensure that all light can be incident into the FP cavity. Among them, the diameter of the inner circle of the ring base 103 is 15-30 μm, the diameter of the outer circle is 35-45 μm, and the thickness is 0.5-2 μm, the length of the spring structure 104 is 20-80 μm, the diameter of the disc chamber plate 102 is 35-45 μm, and the thickness is 0.5-2 μm. 0.5~2μm.

In this embodiment, the diameter of the inner circle of the ring base 103 is 26 μm, the diameter of the outer circle is 34 μm, and the thickness is 0.6 μm, the diameter of the spring structure 104 is 30 μm, and the length is 55.5 μm, and the diameter of the disc cavity plate 102 is 34 μm, and the thickness is 0.6 μm. 0.6 μm.

Preferably, the glass tube 101 is sleeved on one end of the single-mode optical fiber 100 with a 3D micro-nano structure, and the heat-sensitive material 105 is filled inside the glass tube 101 . In this embodiment, the length of the glass tube 101 is 1-2 cm, and the inner diameter is larger than that of the single-mode optical fiber 100 .

Preferably, the heat-sensitive material 105 is a curable material. In this embodiment, the heat-sensitive material 105 is PDMS, and after filling, it is placed at 80° C. for more than 2 hours to fully cure. The curing operation of the heat-sensitive material 105 after filling can enhance the sensor’s stability, mechanical support, and thermal conductivity, while protecting and encapsulating the sensitive material, thereby improving the performance and reliability of the fiber-optic spring-based FP cavity temperature sensor. The choice of polydimethylsiloxane as heat sensitive material 105 can achieve fast curing, excellent dimensional stability, good heat resistance and chemical resistance. These effects help to improve the fabrication efficiency, stability, and reliability of fiber-optic-based spring-loaded FP-cavity temperature sensors.

In this embodiment, the height of the FP cavity along the beam propagation direction (generally the thickness of the ring base 103 plus the height of the spring structure 104 ) is 20.5-82 μm. More preferably, it is 50 to 60 μm.

Therefore, this application can be used to measure ambient temperature.

Fig. 4 is a schematic diagram of the working principle of the optical fiber-based spring FP cavity temperature sensor provided by the present invention. The temperature sensor provided by the present invention mainly adopts the principle of FP cavity interference. As shown in (a) of Figure 4, the light intensities reflected from the fiber end face and the disc cavity plate 102 are respectively denoted as I ₁ and I ₂ , so the interference signals of the two can be expressed as:

where n represents the refractive index of the medium in the cavity (in this case, the refractive index of PDMS), L represents the cavity length of the FP cavity, λ represents the wavelength of the incident light, and _φ0 represents the initial phase. The trough position of the interference spectrum needs to meet the following phase conditions:

where m represents an integer, Indicates the position of the mth order trough. According to formula (2), the temperature sensitivity of the sensor can be expressed as (see (b) in Figure 4):

where optical path difference It can be further deduced as the following formula:

Therefore, combining equations (3) and (4), the temperature sensitivity of the sensor can be expressed as:

In (5) formula represents the thermo-optic coefficient of the cavity medium (i.e. PDMS), /> represents the variation of the unit cavity length with temperature, which is mainly determined by the thermal expansion coefficient of PDMS and the elastic constant k of the spring structure 104 .

As shown in (c) of Figure 4, the thermal expansion of the PDMS in the spring FP cavity will induce the elongation of the spring cavity, which will further bring about the red shift of the interference spectrum, which can be adjusted by changing the elastic constant k of the spring used. , to further adjust the sensitivity S of the sensor. For example, for the same temperature change, a spring with a small k value can be used to obtain a larger cavity length change /> , so as to obtain a higher temperature sensitivity S, which is also the fundamental reason why the temperature sensor has customizable sensitivity.

Fig. 5 is a schematic diagram of the interference spectrum of an optical fiber-based spring FP cavity temperature sensor (prepared with spring constant k=9.9μN/μm) and the displacement of the trough position with temperature changes provided by the present invention. In the experiment, the sensor was placed in an electric oven, and the temperature adjustment range in the electric oven was 30-50°C. The temperatures in the figure were 30, 35.1, 40, 45.1, and 50°C from left to right. The interference spectrum measured by placing the sensor in different temperature environments is shown in (a) in Figure 5, and the temperature sensitivity of the sensor is defined as , where /> is the position offset of the mth order interference trough, /> is the ambient temperature change. It can be seen from (b) in Figure 5 that the interference spectrum is red-shifted significantly as the ambient temperature increases. By linearly fitting the trough position of the interference spectrum and the ambient temperature, the temperature sensitivity of the sensor can be obtained to be about 712.4pm/°C.

Fig. 6 is the repeatability and stability test results of a fiber-based spring FP cavity temperature sensor provided by the present invention. (a) in Figure 6 is the result of three consecutive independent temperature response tests on the same sensor. By linearly fitting the trough position of the interference spectrum with the ambient temperature, the temperature sensitivities obtained are 737.5, 704.3, and 693.1 pm/°C, respectively, and the standard deviation of the three independent test results is only 23.1 pm/°C, indicating that the device has good repeatability . (b) in Figure 6 is the result of placing the sensor in a 30°C incubator for 3 hours to continuously monitor the change of the interference spectrum of the device. The results in the figure show that the interference spectrum of the device does not shift significantly within 3 hours of continuous monitoring, and the standard deviation of the trough position of the interference spectrum is only 66pm, indicating that the device also has good stability.

Fig. 7 is the test result of the relationship between the sensitivity and the spring constant k of the optical fiber-based spring FP cavity temperature sensor provided by the present invention. In this experiment, two-photon polymerization 3D printing technology was used to prepare spring FP cavity structures with different spring constants k on the end faces of optical fibers, and then the cavity was filled with PDMS and packaged to prepare corresponding temperature sensors. (a) in Figure 7 shows that each temperature sensor exhibits a good linear correlation between the trough position of the interference spectrum and the ambient temperature. The relationship between the temperature sensitivity of the device and the spring constant k can be obtained by linear fitting, as shown in (b) in Figure 7. From the figure, it can be seen that the relationship between the temperature sensitivity of the device and the spring constant k can be obtained by a simple Linear correlation description, the fitting slope is -5.8(pm/°C)/(μN/μm). This simple linear relationship makes the sensor have the characteristic of customizable sensitivity, that is, according to the result of (b) in Figure 7, select the appropriate spring k value and prepare the corresponding spring structure 104 on the end face of the optical fiber, people can flexibly customize the sensor with Temperature sensors with different sensitivities, and the sensitivity customization range is 100~700pm/℃.

Fig. 8 is the relationship between the spring constant k and the structural size of the optical fiber-based spring FP cavity temperature sensor provided by the present invention. The elastic constant k of the spring was measured using a modified nanoindenter (Hysitron TM P188). The detailed correspondence between the elastic constant k and its geometric parameters is shown in Figure 8. The geometry of the spring is mainly determined by R, L, t and w marked in the figure. The first three parameters are set to 15 μm, 56 μm and 4 μm respectively, and w is adjusted between 4-14 μm (step size 2 μm) to adjust the elastic constant k of the spring. By adjusting the w value with high precision, the spring k value can be effectively adjusted in the range of about 10-100 μN/μm.

Embodiment two

As shown in Figure 2, based on the same concept, the present application also proposes a method for preparing the above-mentioned optical fiber-based spring FP cavity temperature sensor, including the following steps:

S00, using a two-photon polymerization 3D printing process to print a 3D micro-nano structure on the end face of the single-mode optical fiber 100;

In this embodiment, the processing accuracy of the two-photon polymerization 3D printing process can reach 200nm, combined with high-performance photoresist, it can process a 3D micro-nano structure with a smooth surface and high mechanical strength. The specific preparation steps include: drop-coating photoresist (using negative resist), two-photon photolithography, development, cleaning and ultraviolet (ultraviolet) light curing. The scanning electron microscope representation of the 3D micro-nano structure printed on the end face of the single-mode optical fiber 100 is shown in Figure 2. The size of the structure is basically consistent with the design value, which further demonstrates the high processing accuracy of the two-photon polymerization 3D printing technology.

Wherein, the photoresist used is conventional photoresist, including but not limited to IP-Dip, IP-S and IP-L. In this embodiment, IP-Dip is used as the photoresist.

S10, encapsulating the 3D micro-nano structure in the glass tube 101, injecting the heat-sensitive material 105 and placing it in a vacuum box to allow the heat-sensitive material 105 to enter the FP cavity;

S20, thermally curing the heat-sensitive material 105, so that the heat-sensitive material 105 is completely cured, and the preparation is completed.

In this embodiment, the processing parameters of the two-photon polymerization 3D printing process are:

The two-photon laser parameters used are wavelength 780nm (the optional range is between 700~1000nm), laser power is 16.5mW (the optional range is between 10~20mW), and the laser scanning speed is 170μm/s (the optional range is between 100~20mW). 300μm/s);

The developer used for development is propylene glycol methyl ether acetate (PGMEA);

The cleaning solution used for cleaning is methyl nonafluorobutyl ether (MNE);

The wavelength of violet light used for photocuring is 405nm, the curing temperature is 25°C, and the curing time is 10min.

The specific process is as follows: first, insert the end of the single-mode optical fiber 100 with the micro-nano structure into the glass tube 101 by about 0.5 cm, and fix the end with glue. Then inject PDMS into the glass tube 101, put it in a vacuum box and let it stand for about 30 minutes, so as to promote the PDMS to enter the cavity of the spring FP. Finally, the device was placed at 80 °C for more than 2 h, so that the PDMS was completely cured. So far, the optical fiber-based FP cavity temperature sensor has been prepared. The use of two-photon polymerization 3D printing process to prepare 3D micro-nano structures can achieve the advantages of high precision, complexity, customized design, stability and rapid manufacturing. This helps to improve the performance, reliability, and fabrication efficiency of fiber-optic-based spring FP cavity temperature sensors.

Embodiment three

As shown in Figure 3, this embodiment also provides an optical fiber-based spring FP cavity temperature sensing system, including a tunable laser, an optical fiber connector, an optical power meter, and any of the above-mentioned optical fiber-based spring FP Cavity temperature sensor; the tunable laser is connected to the first end of the optical fiber connector, the second end of the optical fiber connector is connected to the optical power meter, and the third end of the optical fiber connector is connected to the spring FP cavity temperature sensor.

The fiber-based spring FP cavity temperature sensing system has the capability of temperature measurement, the flexibility of tunable lasers, the reliability of fiber optic connectors, the accuracy of optical power meters, and the system integration and portability. These effects contribute to accurate and reliable temperature monitoring and data acquisition.

It should be noted that the tunable laser can provide light of any wavelength. As an experimental example, the wavelength of the light source of the tunable laser is 1500~1630nm. Fiber optic connectors are used to connect fiber optic components, and can be any of fiber optic circulators and fiber optic couplers. The incident light emitted by the tunable laser enters the temperature sensor through the fiber optic connector, and then the reflected light enters the optical power meter again through the fiber optic connector. By scanning the incident wavelength of the tunable laser and measuring the reflected optical power, the corresponding interference spectrum.

It should be noted that, for specific examples in this embodiment, reference may be made to the examples described in the foregoing embodiments and optional implementation manners, and details will not be repeated in this embodiment.

Those skilled in the art should understand that the various technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, all possible combinations of the various technical features in the above embodiments are not described. There is no contradiction in the combination, and all should be considered as within the scope of the description.

The above examples only express several implementation modes of the present application, and the description thereof is relatively specific and detailed, but should not be construed as limiting the scope of the present application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be determined by the appended claims.

Claims (10)

1. A spring FP cavity temperature sensor based on optical fiber, comprising single-mode optical fiber and the 3D micro-nano structure fixed on the single-mode optical fiber end face, is characterized in that, also includes: A glass tube sleeved outside one end of the single-mode optical fiber with a 3D micro-nano structure; heat sensitive material filled in the glass tube; Wherein, the 3D micro-nano structure includes a disc cavity plate arranged for the end face of the single-mode fiber, a ring base connected to the end face of the single-mode fiber, and a ring base connecting the disc cavity plate and the ring base. One or more elastic return parts of the seat, an FP cavity is formed between the end face of the single-mode optical fiber and the disc cavity plate; Wherein, the length of the elastic reset part is driven to change by the thermal expansion of the thermally sensitive material, so as to bring about a red shift of the interference spectrum; Wherein, the adjustment of the elastic constant k is realized by adjusting the geometric dimension of the elastic reset member, so as to realize the adjustment of the temperature sensitivity. 2. A spring FP cavity temperature sensor based on optical fiber according to claim 1, characterized in that, the heat-sensitive material is cured after being filled. 3. A kind of spring FP cavity temperature sensor based on optical fiber as claimed in claim 1, is characterized in that, described 3D micro-nano structure is prepared by two-photon polymerization 3D printing process. 4 . The optical fiber-based spring FP cavity temperature sensor according to claim 1 , wherein when there are multiple elastic reset members, they are evenly arranged along the circumference of the ring base. 5 . 5 . The optical fiber-based spring FP cavity temperature sensor according to claim 4 , wherein each of the elastic reset members is helical. 6 . 6. A kind of spring FP cavity temperature sensor based on optical fiber as claimed in claim 1, it is characterized in that, the outer diameter of described elastic restoring member is greater than the inner diameter of described ring base, and is smaller than the inner diameter of described ring base outside diameter. 7. A spring FP cavity temperature sensor based on an optical fiber as claimed in claim 1, wherein the heat-sensitive material is polydimethylsiloxane. 8. be used for preparing the preparation method of a kind of optical fiber-based spring FP cavity temperature sensor described in any one of claim 1-7, it is characterized in that, comprises the following steps: S00, using two-photon polymerization 3D printing technology to print 3D micro-nano structure on the end face of single-mode optical fiber; S10, encapsulating the 3D micro-nano structure in a glass tube, injecting heat-sensitive materials and placing them in a vacuum box to allow the heat-sensitive materials to enter the FP cavity; S20, thermally curing the heat-sensitive material, so that the heat-sensitive material is completely cured, and the preparation is completed. 9. preparation method as claimed in claim 8 is characterized in that, in S00 step, the processing parameter of two-photon polymerization 3D printing process is: The two-photon laser parameters used are wavelength 700~1000nm, laser power 10~20mW, and laser scanning speed 100~300μm/s; The developing agent that development adopts is propylene glycol methyl ether acetate; The cleaning solution used for cleaning is methyl nonafluorobutyl ether; The wavelength of violet light used for photocuring is 405nm, the curing temperature is 25°C, and the curing time is 10min. 10. An optical fiber-based spring FP cavity temperature sensing system, comprising: a tunable laser, an optical fiber connector, an optical power meter, and an optical fiber-based sensor according to any one of claims 1-7 Spring FP cavity temperature sensor; the tunable laser is connected to the first end of the optical fiber connector, the second end of the optical fiber connector is connected to the optical power meter, and the third end of the optical fiber connector is connected to the optical power meter Spring FP cavity temperature sensor connection.